feat: workspace-based multi-tenancy, replacing user as tenancy axis (#840)

Introduces `workspace` as the isolation boundary for config, flows,
library, and knowledge data. Removes `user` as a schema-level field
throughout the code, API specs, and tests; workspace provides the
same separation more cleanly at the trusted flow.workspace layer
rather than through client-supplied message fields.

Design
------
- IAM tech spec (docs/tech-specs/iam.md) documents current state,
  proposed auth/access model, and migration direction.
- Data ownership model (docs/tech-specs/data-ownership-model.md)
  captures the workspace/collection/flow hierarchy.

Schema + messaging
------------------
- Drop `user` field from AgentRequest/Step, GraphRagQuery,
  DocumentRagQuery, Triples/Graph/Document/Row EmbeddingsRequest,
  Sparql/Rows/Structured QueryRequest, ToolServiceRequest.
- Keep collection/workspace routing via flow.workspace at the
  service layer.
- Translators updated to not serialise/deserialise user.

API specs
---------
- OpenAPI schemas and path examples cleaned of user fields.
- Websocket async-api messages updated.
- Removed the unused parameters/User.yaml.

Services + base
---------------
- Librarian, collection manager, knowledge, config: all operations
  scoped by workspace. Config client API takes workspace as first
  positional arg.
- `flow.workspace` set at flow start time by the infrastructure;
  no longer pass-through from clients.
- Tool service drops user-personalisation passthrough.

CLI + SDK
---------
- tg-init-workspace and workspace-aware import/export.
- All tg-* commands drop user args; accept --workspace.
- Python API/SDK (flow, socket_client, async_*, explainability,
  library) drop user kwargs from every method signature.

MCP server
----------
- All tool endpoints drop user parameters; socket_manager no longer
  keyed per user.

Flow service
------------
- Closure-based topic cleanup on flow stop: only delete topics
  whose blueprint template was parameterised AND no remaining
  live flow (across all workspaces) still resolves to that topic.
  Three scopes fall out naturally from template analysis:
    * {id} -> per-flow, deleted on stop
    * {blueprint} -> per-blueprint, kept while any flow of the
      same blueprint exists
    * {workspace} -> per-workspace, kept while any flow in the
      workspace exists
    * literal -> global, never deleted (e.g. tg.request.librarian)
  Fixes a bug where stopping a flow silently destroyed the global
  librarian exchange, wedging all library operations until manual
  restart.

RabbitMQ backend
----------------
- heartbeat=60, blocked_connection_timeout=300. Catches silently
  dead connections (broker restart, orphaned channels, network
  partitions) within ~2 heartbeat windows, so the consumer
  reconnects and re-binds its queue rather than sitting forever
  on a zombie connection.

Tests
-----
- Full test refresh: unit, integration, contract, provenance.
- Dropped user-field assertions and constructor kwargs across
  ~100 test files.
- Renamed user-collection isolation tests to workspace-collection.

trustgraph-cli/trustgraph/cli/invoke_sparql_query.py

@@ -9,7 +9,8 @@ import sys
 from trustgraph.api import Api
 
 default_url = os.getenv("TRUSTGRAPH_URL", 'http://localhost:8088/')
-default_user = 'trustgraph'
+default_token = os.getenv("TRUSTGRAPH_TOKEN", None)
+default_workspace = os.getenv("TRUSTGRAPH_WORKSPACE", "default")
 default_collection = 'default'
 
 
@@ -44,10 +45,10 @@ def _term_str(val):
     return str(val)
 
 
-def sparql_query(url, token, flow_id, query, user, collection, limit,
-                 batch_size, output_format):
+def sparql_query(url, token, flow_id, query, collection, limit,
+                 batch_size, output_format, workspace="default"):
 
-    socket = Api(url=url, token=token).socket()
+    socket = Api(url=url, token=token, workspace=workspace).socket()
     flow = socket.flow(flow_id)
 
     variables = None
@@ -57,7 +58,6 @@ def sparql_query(url, token, flow_id, query, user, collection, limit,
 
         for response in flow.sparql_query_stream(
             query=query,
-            user=user,
             collection=collection,
             limit=limit,
             batch_size=batch_size,
@@ -154,8 +154,14 @@ def main():
 
     parser.add_argument(
         '-t', '--token',
-        default=os.getenv("TRUSTGRAPH_TOKEN"),
-        help='API bearer token (default: TRUSTGRAPH_TOKEN env var)',
+        default=default_token,
+        help='Authentication token (default: $TRUSTGRAPH_TOKEN)',
+    )
+
+    parser.add_argument(
+        '-w', '--workspace',
+        default=default_workspace,
+        help=f'Workspace (default: {default_workspace})',
     )
 
     parser.add_argument(
@@ -174,12 +180,6 @@ def main():
         help='Read SPARQL query from file (use - for stdin)',
     )
 
-    parser.add_argument(
-        '-U', '--user',
-        default=default_user,
-        help=f'User ID (default: {default_user})',
-    )
-
     parser.add_argument(
         '-C', '--collection',
         default=default_collection,
@@ -228,11 +228,11 @@ def main():
             token=args.token,
             flow_id=args.flow_id,
             query=query,
-            user=args.user,
             collection=args.collection,
             limit=args.limit,
             batch_size=args.batch_size,
             output_format=args.format,
+            workspace=args.workspace,
         )
 
     except Exception as e: